This is a Phase I, multicenter safety study of Factor VIII gene therapy, using a retroviral vector and B-domain deleted factor VIII gene in individuals with severe hemophilia A. Patients must have severe disease, be over age 25, and have no evidence of inhibitors, nor use antiretroviral therapy. Safety and preliminary efficacy parameters will include factor VIII:C level anti-VIIII level, bleeding symptoms and blood chemistries. There will be a pre-treatment 36-hour factor VIII PK study to establish baseline response to infusion. The Factor VIII gene therapy, hFVIII (V) will be given intravenously three consecutive days. A total of 12-20 subjects will be enrolled with graduated dose escalation based on efficacy at the previous lower dose. This study will provide long term follow-up of safety and duration of FVIII response through a Phase I-Extension study, with monthly visits for at least one year after treatment, and thereafter through a lifetime registry with annual visits.